FISH RESEARCH

Otago Daily Times, Issue 26025, 13 December 1945, Page 4

FISH RESEARCH

MORTALITY IN TOMAHAWK LAGOON RESULT OF INVESTIGATIONS Further instances of mortality among trout in the Tomahawk Lagoon were reported recently, and with a view to determining the cause the Otago Acclimatisation Society forwarded samples of the fish and of the water to Mr J. T. Linzey (Benhar), who, prior to his departure from Dunedin, was investigating .conditions in the lagoon. In a report submitted to the society, Mr Linzey said that his examination did not disclose any physical abnormality which might have been the cause of the happenings. All the fish were in good condition and all their internal organs were normal. An examination of the water showed no signs of pollution such as might have been caused by the spent oxide applied to the lupins in the region by the local authorities. The content of salt in the water, he added, was unusually large. The conclusion arrived at by Mr Linzey was that the mortality could not be attributed to any apparent disorder of the trout, nor was it due to pollution of the water in the ordinary sense of the word. The presence of unshed ova, he said, was compatible with the inference that the fish belonged to a water such as Tomahawk Lagoon where spawning facilities were all but absent and would indicate that the fish were not washed in from the E. Percival, of Canterbury College, and Mr Linzey, during an investigation of the condition of the lagoon some time ago, advanced the hypothesis that the decaying weed in the lagoon caused a stratum of gases at a level under the water during a dry spell, and that these were suddenly released by stormy conditions or similar disturbances. On this occasion, however, Mr Linzey found that the nature of the bottom of the lagoon at this time of the year was such that this hypothesis could not have been estab**SMr Linzey added that the only common feature about the three occasions on which the deaths of fish occurred would seem to be the sudden influx of the sea into the lagoon at a time when it was not carrying much water. It was feasible, in his opinion, that a sudden change from fresh to salt water conditions might be fatal to the fish. The investigations are being continued.